I don't like it personally, but I've seen it used to great effect against me. In the base game, I think it's definitely worthwhile, because castles become almost obsolete after age 4 (I've still used them effectively afterwards, but the age 2 / 3 cards pale in comparison power-wise to later cards).
It's most effective in age 1, since 9/15 cards are castles (including metalworking I believe). So if you have a non-castle in your hand, and your opponent melded a non-castle, then I say metalwork away! (There you got either an 8 / 12 or 7 / 12 chance of hitting a castle depending on the achievement).
In echoes, you need to achieve 1 more achievement, so my general power-building strategy starts to pay dividends later. There is an interesting dynamic with chopsticks (which allows you to create more achievements), where I've had five achievements by age 2 or something crazy like that.
Overall, it's not a bad card, and if you can get really lucky and nab monument + 1 / 2 / 3 i'd say you are well on your way to victory. Echoes I wouldn't recommend it personally, but it can also be effective!